1. Field of the Invention
The present invention relates to a double-filament type light source bulb for head lamp, comprising a low beam filament and a high beam filament.
2. Description of the Related Art
As the related art of the light source bulb for head lamp, there can be mentioned Japanese Patent Application Laid-Open No. 2000-164021. In the related art, the light source bulb is a double filament type comprising a low beam filament and a high beam filament in a glass bulb, the low beam filament being connected to first and second support wires, and the high beam filament being connected to second and third support wires.
By rotating the light source bulb, it becomes possible to have a light distribution pattern for the left-hand traffic classification like in Japan, and a light distribution pattern for the right-hand traffic classification in overseas (USA and the like). In either of the distribution pattern, when the low beam filament is lighted, the bottom end becomes the cut line (lighting border plane). Therefore, in the space at the rear of the low beam filament, a virtual image glare light appears in the portion where it becomes dark originally. In order to avoid this phenomenon, the second support wire supporting the low beam filament is bent in an acute angle en route. Since the second support wire is formed of molybdenum material, if it is acutely bent, the elongation percentage differs largely between the inside and the outside in the bent portion. Therefore, needle-shaped bodies are generated on the outside surface, and a finely split condition likely occurs. If such a condition occurs, not only the strength of the second support wire decreases, but also the needle-shaped bodies fall into the glass bulb, causing a problem in that an electrically adverse effect may be caused in the glass bulb.
Moreover, the point of the third support wire is bent towards the inner surface of the glass bulb. Therefore, in the production of the light source bulb, when the third support wire assembled with the high beam filament or the like in advance is inserted into the glass bulb, the bent edge portion may scratch and damage the inner surface of the glass bulb. If a fine damage due to this scratch of the edge occurs in the glass bulb, there is another problem in that the strength of the glass bulb decreases.
It is an object of the present invention to provide a light source bulb for head lamp that prevents the xe2x80x9cfinely split phenomenonxe2x80x9d in the second support wire, and to provide a light source bulb for head lamp that prevents scratch due to the edge of the third support wire.
According to a first aspect of the present invention, there is provided a light source bulb for head lamp used in combination with a reflector, and comprising, in a glass bulb, a low beam filament having the filament axis below the central axis of the glass bulb, and having a front lead and a rear lead, a high beam filament having the filament axis at the obliquely lower side of the filament axis of the low beam filament, and having a front lead and a rear lead, and first to third support wires extending from a bridge to the inside of the glass bulb and located at different vertical positions, the front lead of the low beam filament being connected to the front edge of the first support wire located at a high position, each rear lead of the low beam filament and the high beam filament being connected to the front edge of the second support wire located at the central position, respectively, and the front lead of the high beam filament being connected to the front edge of the third support wire located at a low position, wherein at a curved portion on the extended portion of the second support wire extending from the bridge, a bent portion bent towards the first support wire at an obtuse angle is formed, and each rear lead of the low beam filament and the high beam filament is connected to the bent portion.
According to the first aspect of the present invention, since the bent portion of the second support wire is bent so as to form an obtuse angle, finely split needle-shaped bodies are not generated, unlike the conventional case where it is bent at an acute angle. Moreover, since the bent direction is made to be an obtuse angle with respect to the direction of the first support wire, the bent portion does not intrude into the rear space of the low beam filament where it is optically disadvantageous.
Moreover, the second support wire is arranged towards the third support wire. According to the present invention, since the second support wire is arranged towards the third support wire, the second support wire is away from the first support wire, and even if the bent portion of the second support wire is bent toward the first support wire, it does not come too close to the first support wire, and therefore, the first support wire and the second support wire do not electrically interfere with each other.
The extended portion of the second support wire extending forward from the bridge is inclined at an obtuse angle towards the third support wire. As a result, since the portion of the second support wire extending forward from the bridge is inclined at an obtuse angle towards the third support wire, the bent portion of the second support wire does not come too close to the first support wire, further, and the positions of these support wires can be maintained favorably so that electrical interference does not occur between these wires. The rear lead of the high beam filament can be also fixed to the bent portion with the shortest distance.
A bent portion is also formed towards the second support wire at an obtuse angle, at a curved portion on the extended portion of the third support wire extending from the bridge, and the front lead of the high beam filament is connected to the bent portion. According to this, since the bent portion of the third support wire is directed towards the second support wire at an obtuse angle, when the third support wire is inserted into the glass bulb, the third support wire does not damage the inner surface of the glass bulb, even if it touches the inner surface.
Moreover, the extended portion of the third support wire extending forward from the bridge is inclined at an obtuse angle in the opposite direction to the second support wire.
According to this, since the extended portion of the third support wire extending forward from the bridge is inclined at an obtuse angle in the opposite direction to the second support wire, the bent portion at the front edge of the third support wire does not come too close to the second support wire, and these support wires can be maintained in positions which do not electrically interfere with each other.